The present invention relates to a liquid crystal display device having a backlight for radiating a light-source light on a back surface of a liquid crystal display panel, particularly to the structure which interrupts the intrusion of foreign materials through a gap formed in a joint portion between the liquid crystal display panel and the backlight. To be more specific, the present invention relates to the structure of a joint portion at a corner portion of a resilient member.
A liquid crystal display panel constituting a liquid crystal display device is an image display device which is basically configured such that a liquid crystal layer is sealed between two substrates consisting of a first substrate and a second substrate preferably formed of a glass substrate, and an image is displayed by making use of a change of alignment direction of liquid crystal in response to an electric field applied to the liquid crystal from pixel selection electrodes formed on the substrate. A full transmissive liquid crystal display device which has been most popularly used currently adopts the structure where a light-source light projected from a backlight mounted on a back surface of a liquid crystal display panel is polarized at an angle of approximately 90 degrees, and the polarized light is allowed to pass through a polarizer thus forming an electronic latent image into a visible image which can be observed with naked eyes.
In the image display device using such a non-light-emitting-type liquid crystal display panel, the electronic latent image formed on the liquid crystal display panel is visualized with the use of the external illumination means. The external illumination means is constituted by mounting an illumination device on a back surface or a front surface of the liquid crystal display panel except for the structure which makes use of a natural light. Particularly, a display device which requires high brightness adopts the structure which mounts the illumination device on the back surface of the liquid crystal display panel as a mainstream. Such an illumination device is referred to as a direct back light.
Here, the term “direct backlight” is an expression in contrast with a so-called side-backlight which performs illumination by forming linear light sources having the same constitution on a side of a light guide plate mounted on a back surface of the liquid crystal display panel.
In the liquid crystal display device which uses the above-mentioned direct backlight as the illumination light source, to realize the narrowing of a picture frame, the reduction of weight and the integration of the backlight with the liquid crystal display panel, the liquid crystal display panel is accommodated and held in the inside of a frame-shaped metal frame formed of a metal molded body in a fixed manner, and the metal frame is mechanically fixed to respective sides of a frame-shaped mold casing formed of a resin molded body using bolts or the like in which a diffusion plate, linear light sources, a reflector and the like are accommodated.
The direct backlight is mainly constituted of a reflection sheet arranged to face the back surface of the liquid crystal display panel in an opposed manner, a light diffusion plate arranged on a front-surface side of the reflection sheet, and a fluorescent lamp arranged between the reflection sheet and the light diffusion plate. On these constitutional members, a back plate formed in an approximately trough shape, for example, a side mold frame mounted on the back plate, a frame-shaped mold frame in which the back plate mounting the side mold frame thereon is fitted and the like are stacked in an integral manner thus constituting the direct backlight.
In the backlight having such a constitution, a frame-shaped resilient member such as a silicon rubber sheet is adhered to the frame-shaped mold frame using an adhesive material, and the liquid crystal display panel is mounted on and adhered to an upper surface of the resilient member. Further, in the same manner as the above-mentioned resilient member, a frame-shaped resilient member such as a silicon rubber sheet is adhered to a lower surface of the resilient member using an adhesive material, and are mounted on and adhered to a peripheral portion of the resilient member thus integrally forming the optical compensation sheet stacked body and the diffusion plate with the mold frame.
To be more specific, as shown in FIG. 7 which is a plan view of an essential part of a backlight BL, a diffusion plate DFB arranging an optical compensation sheet stacked body OCS on a back surface side thereof is mounted on the frame-shaped mold frame MLD. A rubber cushion RC constituting a resilient member and applying an adhesive layer to one surface thereof is combined with and adhered to an upper-surface side peripheral portion of the mold frame MLD. Then, the liquid crystal display panel is mounted on the rubber cushion RC to provide the liquid crystal display device.
However, in the liquid crystal display device having such a constitution, a foreign material is adhered to a display screen of the liquid crystal display panel. Accordingly, patent document 1 (JP-A-2003-162901 (corresponding to U.S. Pat. No. 7,283,118)) discloses a backlight and a liquid crystal display device which prevent the intrusion of a foreign material into a display part at the time of exchanging a lamp by mounting a closure member (resilient member) among a diffusion plate, a frame member and a lamp housing thus closing a gap defined between the diffusion plate and the frame member.